Method of treating sour petroleum distillates



Patented June 12, 1951 METHOD OF TREATING SOUR PETROLEUM DISTILLATES John G. Browder, Houston, and Alvin R. Smith,

Baytown, Tex., assignors, by mesne assignments, to Standard Oil Development Company,

Elizabeth, N. 3., a corporation of Delaware No Drawing. Application March 11, 1949, Serial N0. 81,019

14 Claims.

The present invention is directed to a method for treating sour petroleum distillates. More particularly, the invention is directed to the sweetening of sour petroleum distillates in the presence of an alkali metal hydroxide and a mild oxidizing agent.

Prior to the present invention, it has been known to treat sour petroleum distillates with aqueous alkaline solutions, such as solutions of alkali metal hydroxide, to remove hydrogen sulfide and other acidic bodies, following which the sour distillates were treated with sodium plumbite solution to convert deleterious sulfur compounds to compounds which are largely innocuous. This and other prior art processes relied on the addition of sulfur to cause the conversion of the sulfur compounds from mercaptans to disulfides. Other processes convert the undesirable com pounds by means of lead sulfide, which is then separated from the gasoline. Frequently, the separation of lead sulfide from the gasoline was not complete, and, consequently, some Was carried over into storage, which was disadvantageous. Furthermore, the addition of sulfur to gasoline frequently impaired the octane number level of the gasoline since it is well known that sulfur and its compounds affect gasoline detrimentally.

E fforts have been made in the prior art to remedy this situation, and the workers in the field have turned to adding certain compounds, such as phenols and amines, to alkaline solutions, such as sodium hydroxide, to cause conversion through an oxidation mechanism of the deleterious compounds in the sour naphtha. Frequently such expedients are unsatisfactory in not completely sweetening the product, and an aftertreatment, by one of the well known sweetening procedures, becomes necessary.

It has also been known, in the prior art, to employ alcohols in a non-oxidative sweetening process in which small quantities of alcohol are added to the solutions of sodium hydroxide and to the petroleum distillate being sweetened to extract mercaptans from the sour hydrocarbons. In such processes the alcohol is either used as aqueous alcohol dissolved in the alkali metal hydroxide, or the alcohol is added to the caustic solution in large concentrations to provide a solvent which will remove the mercaptans in solution. Thus the prior art teachings have been to the effect in the employment of substantially anhydrous alcohol in conjunction with caustic or in the employment of alcohol in non-oxidative sweetening processes. Such art, on the face,

would appear disadvantageous in obtaining a sweetened product in requiring expensive equipment in view of using large amounts of solvent or in not completely sweetening the product.

From the foregoing discussion of the prior art, it will be seen that the petroleum refining industry has been faced with a problem of converting deleterious sulfur compounds present in petroleum distillates to those which do not detrimentally affect the quality of the product.

It is, therefore, the main object of the present invention to provide a treating process in which improved results are obtained in converting objectionable sulfur compounds to harmless bodies.

Another object of the present invention is to provide an improved sweetening process in which an. active material is added to the petroleum distillate being sweetened to catalyze the conversion of deleterious sulfur compounds.

Another object of the present invention is to provide an improved sweetening process in which small amounts of catalytic reagents are employed.

In the foregoing discussion of the prior art it Will be seen that the prior workers in this field have added compounds such as phenol, amines and alcohols to sweetening processes in which alkaline solutions were employed to treat sour petroleum distillates. We have now found that in distinction to the prior art workers, improved results may be obtained in an oxidative sweetening process in which an alkali metal hydroxide is employed by adding catalytic amounts of alcohols such as methyl or ethyl alcohol. Thus, in accordance with the present invention, the foregoing objects may be achieved by adding to a mixture of sour petroleum distillate and an alkali metal hydroxide a catalytic amount of an aliphatic alcohol While contacting the sour distillate with very small catalytic quantities of a solution of alkali metal hydroxide and maintaining in contact therewith a mild oxidizing agent.

Accordingly, the present invention may be described briefly as involving contacting a sour petroleum distillate having a boiling range of about 50 to 750 F. with a solution of an alkali metal hydroxide to form a mixture thereof While maintaining in the mixture a catalytic amount of aliphatic alcohol, such as methyl alcohol, and adding to the mixture undergoing contacting a mild oxidizing agent in an amount sufficient to sweeten said distillate, following which the alkali metal hydroxide is separated from the contacted distillate.

The aliphatic alcohol finding employment in the practice of the present invention may be illustrated by methyl, ethyl, n-propyl, isopropyl, the 'butyl alcohols, the amyl alcohols, 2-ethyl-nhexanol, and the higher members of the same homologous series. As a general statement, however, it may be mentioned that the low molecular weight aliphatic alcohols will be preferred; in fact, methyl, ethyl and propyl alcohols will be the preferred alcohols used in the present invention.

The alcohols may be employed in amounts based on the naphtha varying from 0.001 to 1.0 per cent by volume, with a preferred range from about 0.01 to 0.15 per cent by volume. It is to be emphasized that the specified amount of alcohol may be added either to the petroleum distillate, to the alkali metal hydroxide solution or to the mixture thereof. Under some conditions, however, it may be preferred to add the alcohol to the naphtha in that a beneficial effect, such as improvement in octane number, may be effected and improved results in color on the sweetened product may be obtained.

The alkali metal hydroxide employed in the present invention preferably should be a solution of an alkali metal hydroxide. Preferably the solution should be an aqueous solution'having a, Baum gravity in the range of from about 30 to about 50 Baum, but solutions of lower strength may be used under some conditions. An aqueous solution of sodium hydroxide of 40 Baum has been found to give satisfactory results in the practice of the present invention. Other alkali metal hydroxides besides sodium hydroxide may be used. For example, lithium and potassium hydroxides may be used in lieu of sodium hydroxide, but the latter is to be preferred.

The temperature at which the treating operation is conducted will usually be atmospheric temperature and may range from about 60 F. up to 200 F. and sometimes higher temperatures may be employed depending on the boiling range and the type of the feed stock being treated. A preferred temperature range may be from about 70 to about 95 F. Satisfactory results have been obtained at atmospheric temperatures encountered in the Texas Gulf Coast area.

The present invention will be further illustrated by the following examples:

Example I A hydrogen sulfide-free high sulfur petroleum distillate which was a raffinate resulting from the sulfur dioxide extraction of a kerosene fraction was divided into five portions. One portion was contacted with a solution of 50 Baum sodium hydroxide in the presence of 300% by volume of the theoretical amount of oxygen required to sweeten. The second portion was also contacted with a 50 Baum solution, but the kerosene had added to it prior to contact 0.5% of methyl alcohol. Similarly, it was contacted in the presence of 300% by volume of the theoretical volume of oxygen required to sweeten. The next three portions had added to them respectively 0.5% by volume based on the kerosene of ethyl, amyl and isopropyl alcohol prior to contacting with the caustic in the presence of 300% by volume of the theoretical amount of oxygen required to sweeten. In each instance the sodium hydroxide solution was separated from the treated kerosene and the treated kerosene was then tested for color and for copper number.

The following table presents the results of the foregoing runs with column 1 presenting the data on the kerosene treated in the absence of an alcohol, whereas the next four columns show '4 the effect of methyl, ethyl, amyl and isopropyl alcohol on the sweetening effect in the presence of an excess of oxygen.

TABLE I 50 B. Caustic ..percent.. 1.0 1.0 l. 0 l. 0 1.0 03, Percent Theor 300 300 300 300 300 Methyl Alcohol .-percent. 0.5 Ethyl Alcohol... ..do 0.5 Amy] Alcohol 0.5 Isopropyl Alcoho 0.5 Cu N 0. before Trea 40 40 40 40 On No. after Treat:

Immediately After 35 7 9 6 25 1 Hour 25 l-2 5 4 24 3 Hours. 0-1 0-1 3 l2 5Hours... 20 Hours. 0-1 Pass 0-1 7. 0

Dr. Per cent Cu N0. Reduction in 20 Hours 50 99 100 99 82. 5 Saybolt Color 22 25 20 21 It will be seen from the data in the foregoing table that the addition of the several alcohols mentioned to the kerosene exerted a beneficial effect in promoting the sweetening reaction. It will also be evident from the results that the color of the treated product was substantially unimpaired in two instances and was improved in one instance. The improvement over the treating operation where the alcohol was absent was approximately twofold.

Example II Since, as pointed out before, the alcohols have been employed in extraction of mercaptans from sour petroleum distillates and in non-oxidative sweetening processes, this example presents a comparison between the practice of the present invention and the prior art in which oxygen was substantially absent.

Seven portions of the kerosene of Example I were obtained and subjected to sweetening procedures, as will be described. One portion was contacted with a 50 Baum sodium hydroxide solution in the presence of 300% of a theoretical amount of oxygen required to sweeten. Another portion had added to it 0.5% by volume, based on the kerosene, of methyl alcohol and was then contacted in the presence of 300% of the theoretical amount of oxygen required to sweeten with a 50 Baum sodium hydroxide solution. This run is the practice of the present invention. Another portion of the kerosene had added to it 0.5% by volume of methyl alcohol and then contacted in the absence of free oxygen with the 50 Baum sodium hydroxide solution. A fourth portion was contacted with the 50 Baum sodium hydroxide solution to which had been added 0.5% by volume based on the kerosene of methyl alcohol in the substantial absence of free oxygen. A similar comparison was made in which ethyl alcohol was added to the kerosene and sweetened in the practice of the present invention with the prior art process of extraction where the ethyl alcohol was added both to the kerosene and to the sodium hydroxide and contacted in the substantial absence of free oxygen.

The results of these seven runs are given in Table II in which the first column shows the results where methyl alcohol was absent; the second column shows the practice of the present invention where methyl alcohol was added to the kerosene; the third and fourth columns show the prior art process of extraction in the substantial absence of oxygen; the fifth column shows the practice of the present invention employing ethyl alcohol added to the kerosene, while the sixth and seventh columns show the comparison of extraction employing ethyl alcohol added either to the kerosene or to the sodium hydroxide solution in the absence of free oxygen.

. 6 24. hours with a much less reduction in color than when the alcohol was absent. Similar results TABLE II Oxygen Oxygen Sweet- Extraction 1D. Extraction 111 ened Present the Absence of igggggg the Absence of Invention Oxygen Invention Oxygen v B. Caustic per cent 1.0 l. 0 1. 0 l. 0 1. 0 1.0 1.0 Oxygen, per cent Th 300 None None 300 None None Methyl Alcohol 0. 0. 5 l 0. 5 None None None Ethyl Alcohol. None None None 0. 5 0. 5 I 0. 5 Copper No. before Treat. 40 40 40 4O 40 Copper N 0. after Treat:

Immediately After 35 9 1 Hour 25 5 3 Hours 0-1 5 Hours. 25 Hours 20 Pass Dr. Per cent 011 N o. R no on 50 100 1 Methyl alcohol added to the caustic and the mixture added to the naphtha. I Ethyl alcohol added to the caustic and the mixture used to extract the naphtha.

It will be seen from the data in Table II that "the practice of the present invention employing either methyl or ethyl alcohol in the presence of oxygen results in substantially complete sweetening of the sour kerosene, whereas the prior art in the absence of the methyl or ethyl alcohol showed about 50% copper number reduction. 'When the extraction was conducted with methyl and ethyl alcohol present, either in the kerosene or in the sodium hydroxide, the greatestreduction obtained in copper number was of the order of 37 /2%, while as little as was obtained, indicating that the presence of free oxygen, as in the present invention, is necessary to obtain a substantially sweet product.

Example III Similar runs were then made with various alcohols employing a hydrogen sulfide-free high sulfur kerosene which was a raffinate resulting from the sulfur dioxide extraction of a kerosene fraction of crude petroleum. A run was made in which the alcohol was absent and runs were made with n-propyl alcohol added both to the kerosene and to the sodium hydroxide. Similar runs were made with isopropyl alcohol added to the kerosene and with Z-ethyl-n-hexanol. In eachinstance, a solution of sodium hydroxide having a gravity of 50 Baum was employed in contacting the kerosene. These results are given in Table III in which the data are arranged in a manner similar to that in Tables I and II.

were obtained with isopropyl alcohol and 2-ethyln-hexanol.

In the foregoing examples, the improvement obtained by the practice of the present invention has been illustrated by the copper number test. This is a well known analytical procedure in the petroleum industry. A description of the method of test may be found in U. 0. P. Laboratory Test Methods for Petroleum and Its Products, 'Third Edition, page 11-61, Universal Oil Products Co., Chicago, 1947. This test is a measureof the mercaptan sulfur content of the oil being tested.

Although not illustrated by the several examples, one of the particular advantages of the present invention resides in the catalytic effect of the alkali metal hydroxide solution. The alkali metal hydroxide appears to function as a true catalyst since the small amount used may be recycled to treat large quantities of the sour petroleum distillate. A small amount of the alkali metal hydroxide solution may be entrained in the treated naphtha, and, therefore, it may be necessary to replace the entrained amount with fresh solution... In short, it is contemplated in the practice of the present invention that the alkali metal hydroxide solution will be reused over and over again since it is not necessary to regenerate the alkali metal hydroxide solution.

The invention has been described and illustrated by employment of a mild oxidizing agent such as oxygen. It is contemplated that mixtures of oxygen with other gases, such as air, may be TABLE III 1345. NaOH, per cent.- 1.0 1.0 1 1.0 1.0 1.0 Theor. Oxygen, Per Cent Theor 300 300 300 300 300 N-propyl N-propyl Isopropyl 2-ethyl n- Promoter None alcohol alcohol alcohol hexanol Amt. of Promoter, per cent 0 0. 5 0. 5 0.5 Copper No. before treat. 33 33 33 33 Color before +22 +22 +22 +22 +22 Copper No. after Treat:

Immediately after 26 20 r 22 21 27 1 hr. after 20 4. 5 6 4.5 15 3 hrs. after 20 3.5 4 3. 5 8. 5 5 hrs. after.. 21 2. 5 2 2. 5 24 hrs. after. 22 0.5 0.5 0.5 4. 0 48 hrs. after. 21 0.5 0. 5 0. 5 2. 0 Color after 24 hrs 5 +8 +5 +17 +7 1 Different from the other treats in that the promoter is added to the caustic and not to the naphtha.

It will be seen from the data in Table III that when no alcohol was present very little copper number reduction was obtained and that the color of the treated product was impaired appreciably,

whereas when n-propyl alcohol was used, either in the kerosene or in the sodium hydroxide, substantially complete sweetening was obtained after understood that the petroleum distillate may be subjected to a preliminary treatment for removal of hydrogen sulfide if the distillate contains hydrogen sulfide. Such preliminary treatment may include washing with a dilute alkali metal hydroxide solution or blowing with a. free-oxygen containing gas such as air. If hydrogen sulfide or other acidic compounds are present and not removed, the alkali metal hydroxide solution employed as the catalyst may very quickly become seriously depleted in activity.

In the practice of the invention, it will be desirable to use an amount of oxygen in excess of the theoretical required to sweeten the sour petroleum distillate. Ordinarily, an amount of about 300% of the theoretical amount to sweeten may be employed. However, sweetening in accordance with the present invention may be obtained with considerably lesser quantities of oxygen. In other instances as much as 500% of the theoretical amount required to sweeten may be employed. In fact, sweetening may be obtained in some cases by contact with the oxygen present in the treating vessel. It will be desirable to employ an amount of oxidizing agent at least equivalent to the theoretical amount required to sweeten.

The invention has been described and exemplified by employment of 0.5 to 1% by volume of the catalytic alkali metal hydroxide solution. It is contemplated that as little as 0.1 and as much as 5% by volume, or more, of the alkali metal hydroxide solution, based on the sour naphtha, may be employed. Very good results, however, are obtained with 1% by volume and this amount will be preferred.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and to secure by Letters Patent is:

1. A method for sweetening a sour petroleum distillate containing mercaptans and boiling below 750 F. while maintaining the color thereof which comprises adding to said sour petroleum distillate no more than 1% by volume of an aliphatic alcohol and then contacting said distillate containing aliphatic alcohol with a catalytic amount not in excess of 5% by volume based on said distillate of an aqueous solution of an alkali metal hydroxide while adding a sufiicient amount of a mild oxidizing agent to convert the mercaptans to disulfides and to obtain a sweetened distillate of unimpaired color.

2. A method in accordance with claim 1 in which the alcohol is methyl alcohol.

3. A method in accordance with claim 1 in which the alcohol is ethyl alcohol.

4. A method in accordance with claim 1 in which the alcohol is a propyl alcohol.

5. A method for sweetening a sour petroleum 0.001% to 1% by volume based on said distillate and then agitating the distillate containing aliphatic alcohol with an amount of an aqueous solution of an alkali metal hydroxide in the range from 0.1% to 5% by volume based on said distillate while add-ing a sufiicient amount of a mild oxidizing agent to convert'mercaptans to disulfides and to obtain a sweetened distillate of unimpaired color.

6. A method in accordance with claim 5 in which the alcohol is methyl alcohol.

7. A method in accordance with claim 5 in which the alcohol is ethyl alcohol.

'8. A method in accordance with claim 5 in which the alcohol is a propyl alcohol.

9. A method for sweetening a, sour petroleum distillate containing mercaptan and boiling in the kerosene range while maintaining the color thereof which comprises adding to said sour distillate 0.5% by volume based on .said distillate of an aliphatic alcohol and then agitating the distillate containing aliphatic alcohol with 1% by volume based on said distillate of a 50 B. aqueous solution of sodium hydroxide while adding a suificient amount of air to convert mercaptans to. disulfides and to obtain a sweetened distillate of unimpaired color.

10. A method for sweetening a sour petroleum distillate containing mercaptans and boiling below 750 F. while maintaining the color thereof which comprises adding to said sour distillate an amount of an aliphatic alcohol in the range between 0.001% and 1% by volume based on said distillate and then agitating the sour distillate containing aliphatic alcohol with an aqueous solution of sodium hydroxide in an amount in the range between 0.1% and 5% by volume based on said sour distillate while adding suflicient air to convert the mercaptans to disulfides, separating said sodium hydroxide from the agitated distillate, and recovering said agitated distillate of unimpaired color.

ll. A method in accordance with claim 10 in which the alcohol is methyl alcohol.

12. A method in accordance with claim 10 in which the alcohol is ethyl alcohfol.

13. A method in accordance with claim 10 in which the alcohol is a propyl alcohol.

14. A method for sweetening a sour petroleum distillate contain-ingmercaptans and boiling in the kerosene range while maintaining the color thereof which comprises adding to said sour distillate 0.5% by volume based on said distillate of isopropyl alcohol and then agitating the distillate containing alcohol with 1% by volume based on said distillate of a 50 B. aqueous solution of sodium hydroxide while adding a suificient amount of air to convert the mercaptans to disulfides and to obtain a sweetened distillate of unimpaired color.

JOHN G. BROWDER. ALVIN B. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,110,283 Archibald Mar. 8, 193.8 2,152,721 Yabrofi Apr. 4, 1939 2,181,037 Wilson Nov. 21, 1939 2,345,449 Birkhimer Mar. 28, 1-944 

1. A METHOD FOR SWEETENING A SOUR PETROLEUM DISTILLATE CONTAINING MERCAPTANS AND BOILING BELOW 750* F. WHILE MAINTAINING THE COLOR THEREOF WHICH COMPRISES ADDING TO SAID SOUR PETROLEUM DISTILLATE NO MORE THAN 1% BY VOLUME OF AN ALIPHATIC ALCOHOL AND THEN CONTACTING SAID DISTILLATE CONTAINING ALIPHATIC ALCOHOL WITH A CATALYTIC AMOUNT NOT IN EXCESS OF 5% BY VOLUME BASED ON SAID DISTILLATE OF AN AQUEOUS SOLUTION OF AN ALKALI METAL HYDROXIDE WHILE ADDING A SUFFICIENT AMOUNT OF A MILD OXIDIZING AGENT TO CONVERT THE MERCAPTANS TO DISULFIDES AND TO OBTAIN A SWEETENED DISTILLATE OF UNIMPAIRED COLOR. 